Integrating DInSAR and modeling to constrain the seismogenic fault of the 2023 Mw 6.8 Al-Haouz earthquake: insights into the Western High Atlas seismotectonics

The integration of remote sensing, modelling methods and field observations has provided promising results in reconstructing a detailed seismotectonic setting referred to an earthquake, mostly for the recognition of the seismogenic tectonic structures and understanding the earthquake mechanism. In this study, a multidisciplinary approach is adopted for the recognition of the seismogenic fault responsible of the 8th September 2023 6.8 Mw Al Haouz earthquake (Western High Atlas, Morocco). Focal mechanisms for the earthquake indicate a compressive event with two nodal plane solutions: a high angle NW-dipping and a low angle SW-dipping plane.

Here, the DInSAR technique has been applied to generate displacement maps for vertical and horizontal (E-W) components for the detection of the coseismic displacement, alongside Okada fault modelling to obtain the theoretical displacement field for both nodal plane solutions. The DInSAR coseismic vertical deformation shows an asymmetric SW-verging uplift of the WHA, bounded to the south by the high-angle NW-dipping Tizi n’Test fault (TnTf). However, the comparison between observed DInSAR-based and the modelled deformation does not conclusively identify the causative fault.

Therefore, elastic modelling using the Triangular Elastic Dislocation (TDE) has been performed to simulate the real fault geometries corresponding to the outcropping faults which better reflect the characteristics of the two proposed nodal plane solutions. In this case, a good match between observed and modelled deformations has been detected for the NW-dipping fault (associable to the TnTf), whereas the SW-dipping fault (associable to the Jebilet thrust, JBt) appears to play a more passive role contributing for a minor amount to the observed deformation.

From the TDE, the Coulomb stress changes have been calculated for the TnTf, and the results have been compared with the aftershock distribution. The good agreement between the positive Coulomb stress changes referred to the NW-dipping fault and the distribution of the aftershocks allows to better constrain the TnTf as causative fault for the 2023 Al Haouz earthquake.

Such integration of observation and modelling methods, therefore, represents a good approach to formulate a novel and detailed reconstruction of the seismotectonic context of the Western High Atlas portion affected by the 2023 Al Haouz earthquake.